FRIDAY, July 14, 2017 (HealthDay News) -- Times of high stress -- Mondays and winter holidays -- seem to be especially hard on the heart, according to new research that suggests these periods are when heart attacks are most likely to occur.

On the flip side, heart attacks are least likely to occur when you're chilling out on the weekend or your summer vacation, the study found.

The findings stem from an analysis of more than 156,000 heart attack cases. They were treated at Swedish hospitals over eight years.

While other factors likely play a role in heart attack risk, stress appears to be a substantial contributor, according to study first author John Wallert, a Ph.D. student at Uppsala University in Sweden.

However, he noted that this study is an observational study, and that means it cannot prove a cause-and-effect relationship. It can only show a link between heart attacks and certain time periods.

The study was published online recently in the American Heart Journal.

Previous research has suggested that highly stressful events, such as earthquakes and World Cup soccer games, may trigger heart attacks. Stress-related heart attacks might also be associated with working life. For example, heart attack rates peak on Mondays and in the morning, the study authors noted.

Changing up the work week is unlikely to have an effect on this phenomenon, other than to possibly change the day that heart attacks peak.

"To scrap the work-week routine would probably be way too drastic. How we in society have agreed on periods of work and rest is actually quite well aligned with our predisposed, internal biological clock, the circadian rhythm," Wallert said in a university news release.

"However, the alignment is not perfect. For instance, our internal clock is highly unlikely to be aware if today is a Monday or a Sunday," he noted.